We shall isolate mutants of Dictyostelium that have a conditionally-defective cyclic AMP chemosensory system. These will be isolated as chemotaxis mutants that fail to migrate through a Millipore filter toward a source of cyclic AMP. A variety of tests will be used to distinguish cyclic AMP receptor mutants from transduction mutants, which fail to transmit the signal to the cytoplasm. Genetic analysis will establish complementation groups and linkage relationships. The plasma membrane of each chemosensory mutant will be examined to determine if an altered component can be associated with the mutant behavior. These studies will permit us to test the hypothesis that periodic, extracellular cyclic AMP signals are part of a controlling system that specifies the pattern of spatial differentiation in Dictyostelium.